<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>aa</title>
</head>
<body>
a和b是同域 http://localhost:5000"
c是独立的 http://localhost:2000"
a获取c的数据
a先引用c c把值放到window.name,把a引用的地址改到b
<iframe src="http://localhost:2000/c.html" frameborder="0" id="frame" onload="load()"></iframe>
<script>
    let first=true;
    function load(){
        if(first){
            let frame=document.getElementById('frame');
            frame.src='http://localhost:5000/b.html'
            first=false;
        }else {
            console.log(frame.contentWindow.name);
        }

    }
</script>
</body>
</html>